Mine waste and waste rock is low-grade material or overburden that has little or no economic value. However, waste rock is not inert. Many of the same physical phenomena that occur in heaps will also occur in waste rock, but the operations of the two piles are much different. First, the solution is not purposely added to extract a resource from waste, and in fact, it is desirable to keep moisture as low as possible. Secondly, drainage that occurs from waste is likely not captured, which can introduce mine impacted waters to the environment with negative consequences. Lastly, they typically have very large grain size, allowing mine impacted water to move quickly from the surface to nearby water sources.
HGI provides the geophysical tools needed to understand the role of mine impacted water moving through waste rock piles. Technologies such as electrical resistivity, IP, and thermal monitoring create new awareness of internal hydraulic processes.
Characterization and monitoring of waste rock can help you to understand the week zones that allow meteoric waters to enter and transport mine drainage. In many situations, such as from metal and coal waste, significant amounts of pyrite will cause the waste to go acidic, which further enhances the transport of heavy metals into the uncontrolled environments. Consequently keeping control of the mine impacted water is critical to eliminating potential environmental damage.
HGI provides the geophysical tools needed to understand the direct consequences of uncontrolled water moving through waste rock piles. Technologies such as electrical resistivity, induced polarization (IP), and thermal monitoring create new awareness of internal hydrology generating actionable information. Electrical resistivity can track the high concentration of iron and other ionic species in water (termed acid rock drainage, or ARD) that are transported through the waste and groundwater. ARD that daylights as seeps along streams can also be traced back to its origination. IP and thermal methods will focus more narrowly on the oxidation of sulfidic minerals, such as pyrite. Together, these geophysical tools can provide the data needed to control, track, minimize or eliminate releases of mine impacted water to the environment.
In the example above, we evaluate a gold waste rock pile due to seep formation. We used electrical resistivity to discover a large conductive anomaly that is responsible for creating the seep. The conductive anomaly represents saturated material. We present two sections of the same line, using a low-resolution pole-pole array and the new Alt Wenner array discussed by Cubbage et al. (2017) <<link to Cubbage paper>>. The Alt Wenner array, developed by HGI, is one of the highest resolution arrays for multi-channel resistivity systems. Notice the additional details offered by the lower section.